The complex formed from the ferric fragment (1-65)H of cytochrome c and apocytochrome c was treated by limited digestion with trypsin in order to remove the redundant residues. The components of the derived complex were separated by ion exchange chromatography in 8 M urea. The three major non-heme and two major heme fragments were tentatively identified as (40-104), (54-104), (39-104), (1-53)H and (1-55)H. Measurements of the fluorescence quenching of tryptophan 59 of the non-heme peptides by the ferric peptides indicated that a 1:1 complex is formed in all 6 cases with a dissociation constant of less than 3 times 10 to the 7th power M. The complex (40-104); (1-53)H, which is obtained in the largest amount, has a Kdiss less than 3 times 10 to the minus eighth power M and approximately 30% of the activity of native cytochrome c when reduced by lactate dehydrogenase from Baker's yeast. Thus cytochrome c can be cleaved at specific sites between residues 39 and 55 and reconstituted as a non-covalent complement with physical and biological properties similar to the parent molecule. This region containing the major sites of permissible trypsin cleavage is the same as that found by R.E. Dickerson et al. to have been excised in Pseudomonas cytochrome c551 during the course of evolution.